Fiber shortening in the inner layers of the left ventricular wall as assessed from epicardial deformation during normoxia and ischemia

A mathematical model of left ventricular mechanics predicts that fiber shortening in the inner layers of the left ventricular wall can be estimated (eendo, est) from the magnitude of minimal (emin, o) and maximal shortening (emax, o) of the outer surface (= epicardium) of this wall. To evaluate this prediction, eendo, est and emin, o were compared with the shortening in the inner layers approximately along the fiber direction (eendo) as measured directly, before and during one minute of coronary artery occlusion. Deformation of the epicardium and the inner layers was determined by measuring mutual motion and angulation of three needles pierced into the myocardial wall, using an electromagnetic inductive technique. The proposed linear relations of eendo, est and emin, o with eendo were found to be significant. The needles hardly influenced wall deformation since similar values of epicardial deformation were found in separate, comparable, experiments (n = 13) using a triplet of epicardial coils. So eendo, est and emin, o are useful estimates of fiber shortening in the inner layers during normoxia and ischemia, especially when the time course of events is followed in the same animal.

Uptake and tissue content of fatty acids in dog myocardium under normoxic and ischemic conditions

The effect of ischemia on the myocardial content of nonesterified fatty acids (NEFA), triacylglycerol, cholesteryl esters, and phospholipids assayed with gas-liquid chromatography was studied in an open-chest dog preparation. Ischemia was induced by partial occlusion of the left interventricular coronary artery during 120 minutes (n = 20). Tissue content of the lipid classes was assessed in biopsies taken from ischemic and normoxic areas of the left ventricular free wall. Local venous blood from the concomitant vein of the left interventricular coronary artery was collected to determine myocardial extraction of lipids. In eight other dogs, no ischemia was induced (control group). Under normoxic conditions, NEFA appeared to be present in trace amounts: about 25 nmol/g wet weight of tissue, representing less than 0.1% of total myocardial fatty acids. During ischemia, NEFA increased in the affected area. This accumulation was most pronounced in the least perfused layer: the subendocardium (up to 172 nmol/g). Blood flow, estimated with radioactively labeled microspheres fell from 0.55 to 0.06 ml/min per g in this particular layer. The uptake of NEFA by the ischemic myocardium was decreased, indicating that enhanced lipolysis of endogenous lipids or reduced combustion may be held responsible for the accumulation of NEFA in ischemic tissue. Since arachidonic and linoleic acids showed the highest relative increase, lipolysis of endogenous phospholipids, rich in these fatty acids, seems to be reasonable. Ischemia had no significant effect on the content of triacylglycerol and cholesteryl esters. Phospholipids tended to decrease in the affected subendocardial layers.

Blood flow distribution in the left ventricular free wall in open-chest dogs

The distribution of blood flow in various layers of the normally perfused left ventricular free wall was studied in open-chest dogs, using 15-micrometer radioactive microspheres. The most pronounced variations were found in epicardial blood flow, which was higher near the apex than near the base and lower along the marginal branch of the left circumflex coronary artery than along the left interventricular coronary artery. The variations in endocardial blood flow were less pronounced, while blood flow in the middle layers was about equally distributed. Consequently the endo/epicardial blood flow ratios varied over the left ventricular free wall. Possible causes of the inhomogeneities in blood flow distribution are discussed.

The effect of elevated arterial free fatty acid concentrations on hemodynamics and myocardial metabolism and blood flow during ischemia

In the present investigation the effect of elevated arterial free fatty acid (FFA) concentrations on regional myocardial blood flow (MBF), myocardial metabolism and hemodynamics during ischemia was studied in anesthetized dogs. Ischemia was induced by stenosis of the left interventricular coronary artery. Mean poststenotic coronary artery pressure was kept constant during ischemia. FFA concentrations were elevated by intravenous injection of heparin (group I), intralipid (group II) or both substances (group III). After elevation of FFA concentrations by heparin alone or together with intralipid, heart rate gradually increased, while aortic pressure tended to decrease. Slight elevation of arterial FFA levels (up to 0.30 mM, group I, and up to 0.53 mM, group II) had no significant effect on total MBF and uptake of glucose, FFA, and oxygen or release of lactate in the ischemic myocardium. However, elevating arterial FFA levels up to 0.81 mM (Group III), significantly decreased total MBF (6%), endo/epicardial blood flow ratio (13%), and oxygen uptake (34%) in the ischemic myocardium and resulted in release of lactate from this area. The release of potassium, inorganic phosphate and H+ as well as plasma CO2 concentration were not influenced. Neither was the uptake of glucose and FFA. These findings suggest that elevated arterial FFA concentrations can decrease MBF and augment lactate production in the ischemic myocardium.